Power converters are used in renewable energy applications to convert electrical power generated by a renewable energy source into power that is suitable for supply to an AC grid. For example, power converters can be used in wind energy applications to convert the alternating current generated by a wind turbine to a desired output frequency (e.g. 50/60 Hz) and voltage level. Power converters can be used in solar energy applications to convert the DC power generated by one or more photovoltaic arrays into suitable AC power for the AC grid.
Power converters typically use a plurality of switching elements, such as insulated gate bipolar transistors (IGBTs), to convert power supplied from an input power source to a suitable output AC power for the AC grid. For instance, the power converters can include a plurality of single-phase bridge circuits, with each bride circuit including an upper switching element and a lower switching element coupled in series. An output of each single-phase bridge circuit can be coupled between the upper switching element and the lower switching element. Each bridge circuit may also include a diode coupled in parallel with each of the upper switching element and the lower switching element.
Existing control systems for power convertors are configured to implement a lockout time (also referred to as interlock time or dead time) when activating and deactivating switching elements, with the lockout time being defined as the amount of time or delay between when the controller sends a turn-off gating signal to one of the switching elements of a single-phase bridge circuit (e.g., the upper switching element) and when the controller sends a turn-on signal to the other switching element within the same single-phase bridge circuit (e.g., the lower switching element). Such lockout time prevents damage to the switching elements by ensuring that the switching elements are never activated or otherwise turned on at the same time.
Since the time required to turn on and/or off a switching element may vary significantly based on the operating conditions of the power convertor (e.g., voltage, current, temperature, etc.), it has been necessary in the past to configure the controller to provide a sufficient lockout time to ensure that there is no overlap in switching element conduction regardless of the operating conditions. Thus, a predetermined lockout time (i.e., a defined time period) is typically programmed into the controller that is sufficient to accommodate even the most extreme operating conditions. Unfortunately, given such required margins, predetermined lockout times are often too long, which can result in additional harmonics in the output waveform as well as an unnecessary delay in the control of the switching elements.
Thus, an improved system and method for controlling the activation and deactivation of switching elements contained within a single-phase bridge circuit of a power convertor would be welcomed in the technology.